EP2632628B1 - Ni-fe-cr-mo alloy - Google Patents

Description

The invention relates to a Ni-Fe-Cr-Mo alloy, in particular a modified alloy according to EN material no. 1.4562.

The alloy with the material no. 1.4562 has on average the following chemical composition (standard values in mass%) Ni 31%, Mn 1.7%, Cr 27%, Mo 6.5%, Cu 1.3%, N 0, 2%.

The DE 32 23 457 A1 relates to an alloy, in particular for producing heavy-duty casings of deep bores or the like with increased resistance to stress corrosion cracking, consisting of C ≤ 0.1%, Mn 3 - 20%, S ≤ 0.005%, Al ≤ 0.5%, Cr 22.5 - 35%, W 0 - 8%, Si ≤1%, P ≤ 0.03%, N 0 - 0.3%, Ni 25 - 60%, Mo 0 - 4%, Cu 0 - 2%, SE 0 - 0.1%, Mg 0 - 0.1%, Ca 0 - 0.1%, Co 0 - 2%. Y 0 - 0.2%, Ti 0 - 0.5%, where
Cr (%) + 10 Mo (%) + 5 W (%) ≥ 50%
½Mn (%) + Ni (%) ≥35 (%)
1.5% ≤ Mo (%) + ½ W (%) <4.

Of the US 5,841,046 a high-strength corrosion-resistant austenitic stainless steel is to be taken, which contains an amount of PREN> 55. An alloy of the following composition (in% by mass) is presented: max. 0.08% C, 0.5-12.5% Mn, 20-29% Cr, 17-35% Ni, 3-10% Mo,> 0.7% N, up to 1.0% Si, to to 0.02% B, up to 0.02% Mg, up to 0.05% Ce, balance iron. At chromium contents between 24 and 28%, nickel contents between 21 and 23% are given, with the PREN amount being between 49 and 65. Of importance in this prior art is the extremely high nitrogen content.

In the US 4,824,638 describes a corrosion-resistant alloy (in mass%) of the following chemical composition: 20.5-32% nickel, 23.5-27.5% chromium, 4-6.7% molybdenum, 0.7-3.6% copper , up to 0.09% Carbon, up to 1.5% silicon, up to 5% cobalt, up to 0.45% nitrogen, up to 1% titanium, up to 0.8% niobium, up to 0.3% rare earths (Ce, La , Mischmetal), up to 2% manganese, up to 1.6% tantalum, remainder iron, the sum of the nickel and cobalt content being between 25.5 and 32% and the chromium content being exceeded by 2 to 6.2%.

By the EP 0 292 061 A1 An alloy has become known with (in mass%) 30 - 32 Ni, 26 - 28 Cr, 0.5 - 1.5% Cu, max. 2% Mn, max. 1% Si, max. 0.2% Al, max. 0.02% C, remainder Fe including unavoidable additions, which also contains 6-7% Mo and 0.1-0.25% N.

The alloy according to EP 0 292 061 A1 has been developed in order to provide a material which is suitable for the production of components which must have a good corrosion resistance, especially against pitting and / or crevice corrosion in aqueous, neutral or acidic media with high chloride ion concentration. It should also be usable for the production of components which must have a removal rate of less than 0.20 mm / a in technical phosphoric acid with a chloride ion concentration of up to 1000 ppm at 100 ° C. It should also be suitable for the production of components which must have a pitting potential of at least 1000 mV _H in aqueous neutral media with a chloride ion concentration of the order of 20,000 ppm at 75 ° C and at least 800 mV _H at 90 ° C. It should also be suitable as a material for producing components in acidic media having a chloride ion concentration of 50,000 ppm and more, such as in a FeCl ₃ solution, a critical pitting temperature of at least 80 ° C and a critical crevice corrosion temperature of at least 50 ° C must have.

As a result, this previously used alloy has more than fulfilled the expectations placed on it in practice. However, the solution annealing temperature for dissolving the brittle sigma phase, which is very high for this alloy, has proved to be disadvantageous. According to VdTÜV Material Data Sheet 509/1, Issue 12.2009 at 1150 to 1180 ° C, with the additional requirement of a subsequent rapid cooling by quenching in water or with the help of compressed air (depending on the wall thickness) such that the temperature range is traversed quickly up to 650 ° C. To ensure perfect resolution of the sigma phase, even with thick-walled components, at least the upper temperature of 1180 ° C must be used in operational practice. There are cases in which such a solution annealing treatment has to be integrated into the manufacturing process, for example when hot-stamping large sheet metal formats in a sandwich package or when hot-pressing thick-walled boiler bottoms. It has been found that the solution cooling and cooling conditions mentioned above can not be complied with insofar as the high pitting and crevice corrosion temperatures due to sigma phase precipitation expected for this alloy are then not achieved.

For alloys (UNS 32654/654 SMO) with similar contents of chromium 24-26% and molybdenum 7-8%, the following empirical formula for the dependence of the sigma solvus temperature in literature (Rechsteiner ETH Zurich Publ. No .: 10647) Found the alloy components: $$\mathrm{T\; sigma}-\mathrm{solvus}=\mathrm{24}.\mathrm{6}\mathrm{Cr}+\mathrm{6}.\mathrm{7}\mathrm{Mn}+\mathrm{50}.\mathrm{9}\mathrm{Not\; a\; word}+\mathrm{92}.\mathrm{2}\mathrm{Si}-\mathrm{9}.\mathrm{2}\mathrm{Ni}-\mathrm{17}.\mathrm{9}\mathrm{Cu}-\mathrm{230}.\mathrm{4}\mathrm{C}-\mathrm{238}.\mathrm{4}\mathrm{N}+\mathrm{447}\left(\mathrm{element\; information}:\mathrm{mass\; percent}\right)$$

Accordingly, the elements chromium, molybdenum, silicon and manganese increase the sigma-solvus temperature; The elements nickel, copper and in particular nitrogen have a lowering effect on the sigma-solvus temperature.

The invention has for its object to provide an alloy that meets the technical requirements described above, without giving up the advantages of the previous alloy.

This object is achieved by an alloy with (in% by mass) Ni 33.5 to 35% Cr 26-28% Not a word 6-7% Cu 0.5-1.5% Mn 1.0-4% Si Max. 0.1% al 0.01-0.3% C Max. 0.01% N 0.1-0.25% B 0.001 - 0.004% SE > 0 to 1%

Fe remainder, including unavoidable impurities.

Advantageous developments of the alloy according to the invention can be found in the associated subclaims.

Surprisingly, it has been found that the above-mentioned high solution annealing temperature range of 1150 to 1180 ° C or higher can be significantly reduced if the nickel content of this alloy is increased to 33.0 to 35.0 mass%. With an average nickel content of 34% by mass compared to previously 31% by mass, the solution annealing temperature range can be lowered by at least 30 ° C. to at least 1120 to 1150 ° C. Furthermore, it has been found that increasing the manganese content by increasing the solubility of nitrogen has a positive effect on the metallurgical stability. Both manganese and nitrogen itself act as stabilizers of the austenitic structure. In addition, manganese binds off sulfur, which impairs the hot workability of the material. Usually, the material 1.4562 is produced with a manganese content of on average about 1.7% by mass. It has now been found that an increase of the manganese content to 1.8 to 2.6% by weight in combination with an addition of nitrogen facilitates the solution annealing treatment by the additional austenite stabilization by lowering the required temperature a little further and shortening the time required can be. Excessively high levels of manganese, however, impair the corrosion resistance, as shown for example in the measurement in the test solution "Green Death".

It is therefore not obvious to increase the manganese content. In fact, in the conducted laboratory melts for manganese metallographic studies revealed the increasing effect on the sigma solvus temperature, but this apparent drawback is removed by improving the nitrogen solubility in the alloy matrix. According to Rechsteiner ETH Zurich, this nitrogen lowers T sigma-solvus and is available for increasing the corrosion resistance to pitting corrosion in chloride-containing media according to the PREN formula as follows. $$\mathrm{PREN}:\mathrm{Cr}+3.3\mathrm{Not\; a\; word}+30N$$

The increased nitrogen solubility due to the defined manganese addition according to the invention leads to a lower binding of the nitrogen to chromium as metal nitride. This increases the effective amount of Cr Cr _eff , which is available to increase corrosion resistance. $${\mathrm{Cr}}_{\mathrm{eff}}=\mathrm{Cr}-\mathrm{10}\mathrm{Cr}\left(\mathrm{C}+\mathrm{N}\right)$$

The effective amount PREN (= mass% Cr + 3.3 mass% Mo + 30 mass% N) from the weighted contents of chromium, molybdenum and nitrogen shall be above the value of 50 for the new alloy as well as for alloy 1.4562. The components made from it should be resistant to intergranular corrosion under the conditions of ASTM G 28, Practice A and, in the solution annealed condition, have a removal rate of less than 0.5 mm / a. Finally, it should also be capable of producing components that need to be free of stress cracking and pitting corrosion under the conditions of an aggressive sour gas test test.

Another feature of the modified alloy according to the invention is the use of rare earths (SE), preferably cerium mischmetal. If these are added to the extent intended, they contribute, in addition to the effectiveness of manganese, to good processability, in particular during hot forming, due to the further setting of sulfur. The contents of SE, in particular cerium misch metal, are between 0.001 and 0.1%. The preferred range is set at about 0.06%.

Cerium mischmetal contains besides cerium lanthanum, neodymium, praseodymium, samarium, terbium and yttrium as well as traces of other rare earth metals.

To improve processability, especially in hot forming, it is proposed to optimize the nickel content and the manganese content starting from a versatile nickel-iron-chromium-molybdenum alloy (EN material N ° 1.4562). In this way, the solution annealing temperature of the sigma phase can be significantly reduced without reducing the resistance of the alloy to technical grade phosphoric acid and other technical acids as well as to pinhole and crevice corrosion attack.

• als Werkstoff zur Herstellung von Bauteilen, die in -wässrigen neutralen oder sauren Medien mit hoher Chloridionenkonzentration eine gute Korrosionsbeständigkeit, insbesondere gegenüber Lochfraß- und/oder Spaltkorrosion aufweisen müssen;
• als Werkstoff zur Herstellung von Bauteilen, die in technischer Phosphorsäure mit einer Chloridionenkonzentration bis zu 1000 ppm bei 100 °C einen Abtragungsrate von weniger als 0,20 mm/a aufweisen müssen;
• als Werkstoff zur Herstellung von Bauteilen, die in wässrigen neutralen Medien mit einer Chloridionenkonzentration in der Größenordnung von 45.000 ppm bei 75°C ein Lochfraßpotential von mindestens 1000 mV_H und bei 90°C von mindestens 800 mV_H aufweisen müssen;
• als Werkstoff zur Herstellung von Bauteilen, die in sauren Medien mit einer Chloridionenkonzentration von 50.000 ppm und mehr, wie z.B. in einer FeCl₃-Lösung eine kritische Lochfraßtemperatur von mindestens 80°C und eine kritische Spaltkorrosionstemperatur von mindestens 50°C aufweisen müssen;
• als Werkstoff zur Herstellung von Bauteilen, die unter den Bedingungen gemäß ASTM G 28, Practice A beständig gegenüber interkristalliner Korrosion sind und im lösungsgeglühten Zustand eine Abtragungsrate von weniger als 0,5 mm/a aufweisen.
• als Werkstoff zur Herstellung von Bauteilen, die unter den Bedingungen eines Sauergas-Prüf-Tests frei von Spannungsriss- und Lochfraßkorrosion sind.

In the following, preferred applications of the alloy according to the invention are given:

• as a material for the production of components which must have a good corrosion resistance, especially against pitting and / or crevice corrosion in aqueous neutral or acidic media with high chloride ion concentration;
• as a material for the manufacture of components which in technical phosphoric acid with a chloride ion concentration up to 1000 ppm at 100 ° C must have an erosion rate of less than 0.20 mm / a;
• as a material for the production of components, which in aqueous neutral media with a chloride ion concentration of the order of 45,000 ppm at 75 ° C must have a pitting potential of at least 1000 mV _H and at 90 ° C of at least 800 mV _H ;
• as a material for the manufacture of components which must have a critical pitting temperature of at least 80 ° C and a critical crevice corrosion temperature of at least 50 ° C in acid media with a chloride ion concentration of 50 000 ppm or more, such as in a FeCl ₃ solution;
• as a material for the manufacture of components that are resistant to intercrystalline corrosion under the conditions of ASTM G 28, Practice A and have a rate of removal of less than 0.5 mm / a in the solution-annealed condition.
• as a material for the manufacture of components which are free of stress cracking and pitting under the conditions of an acid gas test test.

The alloy according to the invention can preferably be used for the production of strips, sheets, bars and forgings, pipes and wires, also as welding wires.

So far only difficult with the alloy according to material no. 1.4562 due to the high solution annealing temperature producible roll or blast plated components can now be made easier by the reduced solution annealing temperature.

Table 1 discloses exemplary embodiments of the inventively molten alloy (LB 2151), a large-scale melt (Nicrofer 3426 hMo) and a prior art alloy (LB 2149), in particular their chemical compositions and test results. Table 1 LB 2149 (figures in%) LB 2151 (in%) Nicrofer 3426 hMo (135755) Ni 31.78 33.84 33.79 Fe 30.8 (R) 29.52 (R) 29.16 (R) Cr 27.93 26.74 26.38 Not a word 6.16 6.67 6.88 Cu 1.13 1.27 1.16 Mn 1.54 1.54 1.97 Si 0.04 0.04 0.05 al 0.15 0.04 0.04 N 0.18 0.194 0.21 C 0,022 0.0024 0,007 S 0.0046 0.0015 0,002 B 0,003 0,004 0,003 SE 0.07 0.02 0.02 Co 0.14

The laboratory batch LB 2149 has a content of Ni outside the claimed Ni range.

metallography:

The microstructure is free of sigma phase and fully recrystallized.

Mechanical values sheet metal 22 mm:

Tensile test at room temperature : transverse samples Sheet 22 mm Nicrofer 3426hMo # 135755 Yield strength Rp _0.2 N / mm ² Yield point Rp _1.0 N / mm ² Tensile strength Rm Fracture A _man % 330 371 708 59 hardness measurement
HRB 84
Notched impact: transverse samples
262 Joules (Av)
Corrosion measurements critical pitting temperature in the "Green Death":

The investigations of the critical pitting temperature in the test medium Grüner Tod have shown that the target temperature of 55 ° C was exceeded.

The calculated effective PREN from the chromium, molybdenum and nitrogen for the alloy according to the invention is PREN = 54, and thus, like the known alloy 1.4562, has a value above 50.

Critical Pitting Temperature to ASTM G48 C:

Samples from the 22 mm rolled sheet achieved a critical pitting temperature between 90 and 100 ° C in the ASTM G48 C test. Samples of material 1.4562 from a 5mm sheet as a comparison reached a maximum temperature of 95 ° C in this test.

Corrosion test ASTM G 28, Practice A (intergranular corrosion):

As a result, the value was 0.19 mm / a, and no intergranular corrosion was found in the cut.

Claims (10)

1. An alloy comprising (in % by mass) Ni 33.5 - 35 % Cr 26 - 28 % Mo 6-7 % Cu 0.5 - 1.5 % Mn 1.0 - 4 % Si max. 0,1 % Al 0.01 - 0.3 % C max. 0.01 % N 0.1 - 0.25 % B 0.001 - 0.004 % rare earths > 0 to 1 % Fe being the rest, including unavoidable impurities.
2. An alloy according to claim 1, characterized in that the Ni content (in % by mass) is comprised between 33.5 and 34.5 %.
3. An alloy according to claim 1 or 2, characterized in that the Mn content (in % by mass) is comprised between 1.5 and 3.5 %.
4. An alloy according to one of the claims 1 through 3, characterized in that the Mn content (in % by mass) is comprised between 1.5 and 3.0 %.
5. An alloy according to one of the claims 1 through 4, characterized in that the Mn content (in % by mass) is comprised between 1.5 and 2.6 %.
6. An alloy according to one of the claims 1 through 5, characterized in that the manganese content (in % by mass) is comprised between 1.5 and 2.0 %.
7. An alloy according to one of the claims 1 through 6, characterized in that the nitrogen content (in % by mass) is comprised between 0.14 and 0.22 %.
8. An alloy according to one of the claims 1 through 7, characterized in that the rare earths are formed by contents comprised between 0.001 and 0.1 % of a cerium composition metal.
9. An alloy according to claim 8, characterized in that the total of rare earths is max. 0.06 %.
10. An alloy according to one of the claims 1 through 9, characterized in that the pitting index PREN (=% by mass Cr + 3.3 % by mass Mo + 30 % by mass N) is ≥ 50, especially ≥ 54.

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